4.3 V6 to 5.0 V8 swap questions?

[divorced]

I have a '95 C1500 with a TBI 4.3 and 4L60E transmission. I have a TBI 305 from a '89 C1500 with a 700R4. I want to put the 305 in my truck and still use the 4L60E, but have a few questions:

1. I look at the exhaust manifolds and they appear to connect to the y-pipe in the same location. Will the 305 manifolds connect to the 4.3 y-pipe?

2. Does my computer control my 4L60E transmission? My truck has a 4L60E, the donor truck had a 700R4. Will the computer chip from the 305/700R4 computer work with the new 305/4L60E combo? Or will I need a 305/4L60E chip?

3. Are the engine wiring harnesses any different?

4. Will my tachometer for the 4.3 work with the V8? Will it be accurate?

5. Any comments or suggestions are welcome.

My truck has a good running 4.3 with 190,000 miles, but I want to swap to a V8 for more power. The 305 will be fine for now until I can swap in a built 350.

Thanks.

 

[dyeager535]

4L60E is computer controlled. The older ECM will not work with the tranny, but if the 5L was offered at the same time, a 4.3 and 5.0 ECM are likely the same, you'd just need the right chip, or make one.

Over on thirdgen.org, perhaps here, I've posted a link to a site that helps you find what ECM/BCC your vehicle had originally, so you could compare the '95 4.3 and 5.0 ECM number.

 

[jhellwig]

It isn't going to be as simple as swaping computer chips. The 95 is could be a vortech and could have OBD2 electical system while the 89 will have the old system. I am not sure on the what it would have but gm was starting to change its vehicals over in 95.

 

[dyeager535]

Changeover to Vortec en masse was supposedly 1996. I know people say Vortec in 1995 in some cases, but I *really* don't see that happening...that's an entirely different injection system and would have meant separate EPA certification. I *have* seen Vortec 4.3 engines in late 80's early 90's Astros (enough to believe they were stock) HOWEVER, I have never seen what they were...TBI or CPI. I have a sneaking suspicion they were nothing but TBI with Vortec on the valve covers.

I also doubt any TBI stuff was ever OBD2. Perhaps on some of the stuff that was over 1 ton, but TBI was dead AFAIK on every GM car/light truck by 1996. All you have to do is compare the ECM numbers to prove one way or the other.

 

[divorced]

I have a sneaking suspicion they were nothing but TBI with Vortec on the valve covers.

Thanks for the info Dorian. The quote above is exactly what my '95 is - just the word "Vortec" on the valve covers on a TBI engine. I still have the computer from the '89 5.0 and the complete wiring harness. The 5.0 was available in '95, so it sounds like it souldn't be a problem to make it all work.

Do you know if my tachometer for the 4.3 will work with the V8? And will it be accurate?





.

 

[dyeager535]

I doubt the tach will work because the Astro's never had V8's stock, so no point in making the tach switchable between 6 and 8 cylinders. Unless the same tach was used on something that WAS 8 cylinders.

GM did this on at least their 1980's cars, just a switch that you moved to go from 6 to 8 cylinders, same tach for either cylinder number.

 

[73k5blazer]

my 1986 c10 sales brochure with the 4.3lV6 says vortec, it's misleading, those heads are really choked up. 1996 was the year the "real" vortec heads were used.
BTW, 1985,86 c10 trucks with 4.3lV6 were carbed(i have an '86), just an option if you wanted to ditch all the computer stuff. You could always buy the edlebrock carbed intake manifold too. Don't know how you'd control your 4l60e though.

 

[MattK]

if i were you id just save my time and money until i had a 350 ready to go in.

the difference between the 4.3 and older 5.0 isn't all that great.

 

[dave_90_blazer]

put the 305 in, but use the 4.3 sensors and wiring, use the 305 distributor and nothing else

the 4.3 wiring should be plenty long enough to go a couple more inches, might even be the same as the v8 harness

you need to use the 4.3 wiring because the trans wiring is part of it

the computer was the same, just need the right chip/software